Display Device and Light Adjusting Method Thereof

ABSTRACT

The invention provides a display device and a light adjusting method thereof capable of carrying out light adjustment effectively by the output control of a light source and, preferably, of effecting light adjustment according to color distribution of a displayed image. The display device of the invention that is capable of adjusting a displayed image by changing light flux can include a plurality of light sources having light emitting diodes, an image analyzing unit for outputting a light control signal for controlling the output of each of the light sources, based on an image signal of the displayed image, and a light control device for controlling the output of each of the light sources based on the light control signals.

This application is a continuation of U.S. patent application Ser. No.10/817,806, filed on Apr. 6, 2004, which claims priority to JapanesePatent Application No. 2003/118227, which was filed in the JapanesePatent Office on Apr. 23, 2003. The disclosures of the priorapplications are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a display device and a light adjustingmethod thereof.

2. Description of Related Art

A conventional projection type display device can have the followingproblems. Because of leaked light or stray light that occurs in severaloptical elements constituting an optical system, sufficient contrast isnot obtained. That is, the displayable brightness range (dynamic range)is narrow, and image quality is inferior as compared to an existingimage monitor using a cathode ray tube (hereinafter, referred to asCRT). Although quality improvement of an image is sought by variousimage signal processes, it is impossible to exhibit sufficient effectsbecause of a fixed dynamic range.

As a solution for the problems associated with such a projection typedisplay device, namely, a method of expanding the dynamic range, it canbe considered to change the flux of a light component incident to thelight modulating means (light valve) according to an image signal. Themost convenient method for realizing it is to change the light outputintensity of a lamp. A method of effecting control of the output lightcomponent of a metal halide lamp in the projection type liquid crystaldisplay device is disclosed, for example, in Japanese Unexamined PatentApplication Publication No. 3-179886. Further, because light emittingspectral variations by which output variation is accompanied in thewhite light source occurs, effecting the display by correcting it hasbeen proposed, for example, in Japanese Unexamined Patent ApplicationPublication No. 11-296127.

SUMMARY OF THE INVENTION

However, although a technique described in the Japanese UnexaminedPatent Application Publication No. 11-296127 is employed, light emittingspectral variation of a white light source is complicated and a largesized correcting circuit is required. Further, in cases in which thereis deflection in color distribution of a displayed image, efficientlight adjustment in a white light source cannot be carried out, and theneffects by light adjustment cannot be sufficiently obtained.

It is an object of the invention to provide a display device and a lightadjusting method thereof capable of effectively carrying out lightadjustment by the output control of light sources and, preferably, oflight adjustment depending on the color distribution of a displayedimage.

A display device of the invention that is capable of adjusting adisplayed image by changing the illuminating light flux, ischaracterized in that it can include a plurality of light sources havinglight emitting diodes, image analyzing device for outputting a lightcontrol signal for controlling the output of each of the light sourcesbased on an image signal of the displayed image, and light controldevice for controlling the output of each of the light sources based onthe light control signals.

According to the display device, in order to carry out a display bychanging the illuminating light flux, a light control signal is setbased on the image signal inputted to the image analyzing device, andthe output of the light emitting diode element is controlled by thelight control device based on the light control signal so that the lightemitting amount is changed, thereby carrying out accurate lightadjustment with good control. Further, because excellent temporalcontrollability is possible by a high speed response of the lightemitting diode element, the device can be very suitably employed as aprojection type display device of a color sequential manner for carryingout a display by modulating time-divisionally different colored lightcomponents.

Further, it is possible to provide a projection type display device withhigh reliability in a simplified construction, since it is unnecessaryto consider reliability or durability such as deterioration of the lightadjusting element due to light irradiation or deterioration of amechanical structure of the shutter, as in the case of carrying outlight adjustment by blocking light from the light source using a liquidcrystal light adjustment element, a mechanical shutter or the like.

The display device of the invention may have a construction in which theimage analyzing device outputs the light control signal based on theaverage of the image signal inputted in a predetermined period. Bycalculating the image processing parameter using this average value as afeature, it is possible to carry out light adjustment without losing theatmosphere of the image viewed by an observer.

The display device of the present invention may have a configuration inwhich the image analyzing device outputs the light control signal basedon the maximum of the image signal inputted in a predetermined period.Because the maximum value of luminance can be shared with an expansioncoefficient (expansion parameter), it is possible to simplify theconstruction of the image analyzing device and it is possible to lowerthe cost. In addition, there is an advantage that, since an image areawhere gray tone collapse occurs due to the expansion process can besuppressed to a minimum, it is possible to obtain a display faithful toan inputted image signal.

The display device of the invention may have a construction in which theimage analyzing device outputs the light control signal based on theluminance distribution of the image signal inputted in a predeterminedperiod. By setting the light control signal based on a luminancedistribution, it is possible to set an image processing parameter withmore a carefully considered display area while avoiding an unexpecteddata, such as a noise, and to effectively suppress a flickering screendue to light adjustment.

The display device of the invention may have a construction in which thesignal resolution (bit width) of the light control signal inputted tothe light control device is made different according to the relativeluminous efficiency of a colored light component outputted from theplurality of light sources. It is possible to carry out effective lightadjustment with respect to a user by adopting such a configuration.

Further, it is preferable that the display device of the invention mayhave a construction in which the signal resolution of the light controlsignal corresponding to a green colored light component of colored lightcomponents outputted from the light sources is larger than that of thelight control signal corresponding to other colored light components.

The signal resolution of the light control signal becomes higher withrespect to the light source for outputting the green colored lightcomponent with a human's high relative luminous efficiency, and outputcontrol is carried out more finely, resulting in improvement insubstantial gray scale display to the observer. In other words, becauseit is possible to allow an observer to recognize fine control ondifferent colors by carrying out fine control on a color with a highrelative luminous efficiency in which an observer sensibly recognizes avariation in luminance or chroma, it is possible to simplify theconstruction of the drive circuit as compared to a case of improving thesignal resolution of the light control signal corresponding to threecolors, and to realize a projection type display device with excellentgray scale display at a low cost.

The display device of the invention may have a construction includingthe output balance correcting means for executing a signal correctingprocess on the image control signal in order to correct the whitebalance of the displayed image. With this construction, it is possibleto provide a display device in which white balance variation of thedisplayed image due to light adjustment can be prevented effectively,and a high definition displayed image can be obtained.

Further, the display device of the invention may have a construction inwhich the output balance correcting means comprises a lookup tableincluding output property information of each of the light sources. Withthis construction, it is possible to provide a display device in whichcorrection of the output balance can be carried out flexibly and rapidlyusing the lookup table, and a high quality image can be obtained.

Next, the display device of the invention, which is capable of adjustinga displayed image by changing the illuminating light flux, can becharacterized in that it includes a plurality of light sources havinglight emitting diodes and capable of outputting different colored lightcomponents, a light modulating device disposed correspondingly to eachof the light sources for modulating each of the colored lightcomponents, an image analyzing device for outputting a plurality oflight control signals for controlling the output of each of the lightsources based on a color signal corresponding to each of the coloredlight components included in the image signal of the displayed image,and a light control device for controlling the output of each of thelight sources based on the light control signals.

According to this display device, in order to carry out a display bychanging the illuminating light flux, the output of the light emittingdiode element is controlled by a light control signal based on theinputted image signal, the light emitting amount thereof is changed, andthe light control signal is independently set for each color signal, sothat accurate light adjustment is carried out easily. In addition, evenin cases in which there is deflection in color distribution of thedisplayed image, it is possible to carry out light adjustment veryeffectively. Needless to say, excellent temporal controllability is alsopossible by the high-speed response of the light emitting diode element,and it is possible to always obtain an improvement effect of reliabilitydependent on an unnecessary light-adjusting element such as a shutter.

The display device of the invention may have a construction in which theimage analyzing device outputs each of the light control signals basedon the average of each of the color image signals inputted in apredetermined period. By calculating the image processing parameterusing this average, it is possible to carry out light adjustment withthe impression of the original image.

The display device of the invention may have a construction in which theimage analyzing device outputs each of the light control signals basedon the maximum of each of the color image signals inputted in apredetermined period. Because the maximum value of luminance can beshared with an expansion coefficient (expansion parameter), it ispossible to simplify the construction of the image analyzing device andit is possible to lower the cost. Further, there is an advantage inthat, since an image area where gradient is saturated due to theexpansion process can be suppressed to a minimum, it is possible toobtain a display faithful to an inputted image signal.

The display device of the invention may have a construction in which theimage analyzing device outputs each of the light control signals basedon the luminance distribution of each of the color signals inputted in apredetermined period. By setting the light control signal based on aluminance distribution, it is possible to set an image processingparameter with a more carefully considered display area while avoidingan unexpected data portion such as a noise, and to effectively suppressa flickering screen due to light adjustment.

The display device of the invention may have a construction in which theimage analyzing device sets each of the light control signals using adifferent value for each of the color signals. By allowing the featurefor setting the light control signal to be changed for each color signalas described above, it is possible to set a light control signal moreflexibly and properly, thereby promoting improved image quality withlight adjustment.

The display device of the invention may have a construction in which theimage analyzing device is able to output an image control signal formodulating the image signal, and the device can include image processingdevice for modulating the image signal of the displayed image based onthe image control signal. With this construction, since the display iscarried out by effecting an image process based on image analysis by theimage analyzing device, it is possible to obtain a high quality displaysuitable for the light adjustment display. Further, since imageprocessing is possible for darkening a black display portion by offsetprocessing, effects by the light adjustment display is further promoted,thereby promoting high quality.

Next, a light adjusting method of a display device capable of adjustinga displayed image by changing the illuminating light flux ischaracterized in that it includes, in order to control the fluxes oflight components irradiated from a plurality of light sources havinglight emitting diodes to light modulating device, an image analyzingstep of outputting a light control signal for controlling the output ofeach of the light sources based on the image signal of the displayingimage, and a light control step of controlling the output of each of thelight sources based on the light control signals. With this lightadjusting method, since the light control signal based on the inputtedimage signal is outputted in the image analyzing step, and the output ofthe light emitting diode element is controlled in the subsequent lightcontrol step so that the light emitting intensity thereof is changed, itis possible to carry out accurate light adjustment easily, and also toperform high speed light adjustment due to the high speed response ofthe light emitting diode element.

It is preferable that in the light adjusting method of the invention,the image analyzing step outputs the light control signal with differentsignal resolutions according to the relative luminous efficiency of acolored light component outputted from the light source. By allowing achange of signal resolution of the light control signal according to ahuman's relative luminous efficiency as described above, it is possibleto realize improvement, and to obtain an excellent display image qualityin practical at a low cost.

It is preferable in the light adjusting method of the invention toadjust the white balance of the displayed image by adjusting the outputbalance of each light source when the output of the light source iscontrolled in the light control step. With this method, color tonevariation upon light adjustment due to the output property of the lightsource can be prevented effectively, thereby obtaining a high qualitylight adjustment display.

Next, a light adjusting method of a display device of the invention,which is capable of adjusting a displayed image by changing theilluminating light flux, can be characterized in that it includes, inorder to the control flux of a light component irradiated from aplurality of light sources having light emitting diodes for emittingdifferent colored light components to light modulating means disposedcorrespondingly to the plurality of light sources, an color analyzingstep of outputting a light control signal for controlling the output ofeach of the light sources based on a color signal corresponding to eachcolored light component included in the color signal of the displayedimage, and a light control step of controlling the output of each of thelight sources based on the light control signals.

With this method, since the light control signal based on the inputtedimage signal is outputted in the image analyzing step, and the output ofthe light emitting diode element is controlled in the subsequent lightcontrol step so that the light emitting amount thereof is changed, it ispossible to effect accurate light adjustment easily, and also, since thelight control signal for controlling the output of the light source isset based on analysis for each image signal, it is possible to carry outlight adjustment very efficiently even though there is deflection incolor distribution of the displayed image.

In the light adjusting method of the present invention, the lightcontrol signal can be set based on different values for each of thecolor signals upon setting the light control signal in theimage-analyzing step.

By applying the different value for setting the light control signal foreach image signal as described above, it is possible to set the lightcontrol signal more flexibly and properly, and to promote image qualityimprovement of the displayed image upon light adjustment.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numerals reference like elements, and wherein:

FIG. 1 is a schematic configuration diagram of a projection type displaydevice of a first embodiment;

FIG. 2 is an exemplary block diagram of a drive circuit of theprojection type display device as shown in FIG. 1;

FIG. 3 is an exemplary block diagram of an image-analyzing portion;

FIG. 4 is an example of a histogram according to the first embodiment;

FIG. 5 is an exemplary block diagram of an image-processing portion;

FIG. 6 is an example of another construction of the projection typedisplay device according to the first embodiment;

FIG. 7 is an exemplary block diagram of a drive circuit according to asecond embodiment;

FIG. 8 is an exemplary block diagram of an image-analyzing portion; and

FIG. 9 is an example of a histogram according to the second embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments of the invention will be described withreference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram of a projection type displaydevice, which is a first embodiment of a display device according to theinvention. A projection type display device 30, shown in FIG. 1,comprises light sources 2R, 2G and 2B, each capable of emittingdifferent colored light component, liquid crystal light valves (lightmodulating means) 22 to 24, a dichroic prism 25, and a projection system26. A reference numeral 27 is a screen on which an image is projectedand displayed.

The light source 2R is composed of a lamp 7R for emitting a red coloredlight component LR, and a reflector 8 for reflecting the light of thelamp 7R. The light source 2G is composed of a lamp 7G for emitting agreen colored light component LG, and a reflector 8 for reflecting thelight of the lamp 7G. The light source 2B is composed of a lamp 7B foremitting a blue colored light component LB, and a reflector 8 forreflecting the light of the lamp 7B. The lamps 7R, 7G and 7B can includean LED (light emitting diode) element that emits each of the coloredlight components.

The light sources 2R, 2G and 2B are disposed correspondingly to theliquid crystal light valves (light modulating means) 22, 23 and 24.

The red colored light component LR emitted from the light source 2R isincident to the liquid crystal light valve 22 for the red colored lightcomponent, where it is modulated. The green colored light component LGemitted from the light source 2G is incident to the liquid crystal lightvalve 23 for the green colored light component, where it is modulated.The blue colored light component LB emitted from the light source 2B isincident to the liquid crystal light valve 24 for the blue colored lightcomponent, where it is modulated.

Three colored light components modulated by respective liquid crystallight valves 22, 23 and 24 are incident to the cross dichroic prism 25,where the three colored light components are mixed to form a lightcomponent representing a color image. The mixed light component isprojected onto the screen 27 by a projection system 26 composed ofprojection lens or the like, so that an enlarged image is projected.

An image processing unit (not shown in FIG. 1) for carrying out apredetermined image process on each colored light component is connectedto each of the liquid crystal light valves 22 to 24, and the imagesignal subject to the predetermined image process in the imageprocessing unit is supplied via a light valve driver to each of theliquid crystal light valves 22 to 24. Further, an image analyzing unit(not shown) is connected via a light control driver to each of the lightsources 2R, 2G and 2B, and is adapted to control the output of each ofthe light sources 2R, 2G and 2B based on the analysis of the imagesignal by the image analyzing unit.

The projection type display device according to the present embodimentcarries out an image display based on the image process in the imageprocessing unit and the output control (light adjustment) of the lightsource by the image analyzing unit and the light control driver.

Next, a light adjusting method applied to the projection type displaydevice of the present embodiment will be described. FIG. 2 is a blockdiagram representing a drive circuit of the projection type displaydevice as shown in FIG. 1.

First of all, an image signal is inputted to an image processing unit(image processing means) 31 and an image analyzing unit (image analyzingmeans) 34. The image analyzing unit 34 calculates an image processingparameter such as an expansion coefficient and an offset value byperforming an analysis of the image signal, and supplies it as an imagecontrol signal to the image processing unit 31. The image processingunit 31 performs a predetermined image process on the image signal basedon the received image control signal, and then, inputs it to the lightvalve drivers 12 to 14. The light valve drivers 12 to 14 controls theliquid crystal light valves 22 to 24 for each colored light componentbased on the received image signal.

Further, the image analyzing unit 34 controls light control drivers 15and 16 based on the light control signal. These light control drivers 15to 17 control respective corresponding light sources 2R, 2G and 2B, andcontrol outputs of the respective light sources to change the amount oflight component irradiated to liquid crystal light valves 22 to 24.Here, the light flux is the light flux for about one unit of time, andas a method for changing the light flux, there are, for example, amethod for continuously emitting the light component by changing thelight emitting intensity, a method for changing the light emittingperiod in which the intensity is constant, and a method for changingboth the light emitting intensity and the light emitting period.

In other words, the projection type display device of the presentembodiment analyzes the displayed image by means of the image analyzingunit 34, changes the flux of the light component irradiated from thelight source, and keeps the overall image luminance with a predeterminedimage process (expansion process) by the image processing unit 31, sothat a dynamic range of the liquid crystal light valve is fully used toeffect a display, thereby realizing smooth rich tone. Further, because ablack level (zero signal level) can be darkened by reduced light flux,it is possible to obtain a high contrast image darkened.

The image analyzing unit 34, as shown in an exemplary block diagram inFIG. 3, can include a histogram-producing unit 36 and ahistogram-analyzing unit 37. The histogram-producing unit 36 produces ahistogram (frequency distribution for occurrence) for gray scale level,as shown in FIG. 4, from image data of the image signal inputted in apredetermined period (e.g., one frame). In FIG. 4, a horizontal axisindicates a gray scale level and a longitudinal axis indicates thenumber of pixels.

The produced histogram is supplied to the histogram-analyzing unit 37,and this histogram-analyzing unit 37 extracts characters of thedisplaying image from the received histogram, and calculates anexpansion coefficient, an offset value or the like, which becomes animage processing parameter in the image processing unit 31, based onthis feature.

The character, which can be extracted by the histogram-analyzing unit37, includes the average value of, the maximum value of the luminance,the minimum value of the luminance, or the like. An operation of settingthe image processing parameter based on each character is shown in thefollowing (1) to (3).

(1) The average of the image signal represents most simply thebrightness of the image. By an image processing parameter calculatedusing this average value, light adjustment can be carried out keepingthe impression of the image. Further, because the average of the imagesignal can be obtained without producing a histogram, it is advantageousto simplify the construction of the image-analyzing portion 34.

Although as the average value of the luminance, the average of allpixels included in the image signal can be adopted, it is possible toapply a method of adopting the highest average value as an imageprocessing parameter (expansion coefficient) from the plural averagevalues for each area made by dividing the image of one frame, andcomparing these average values.

(2) In the case of using a parameter that can be obtained from theluminance distribution of the image signal as a feature, the maximumfrequency value of luminance distribution, a luminance value separatedby a predetermined pixel number from maximum luminance (or a minimumluminance) or the like can be used. In the case of using these features,it is possible to set an image processing parameter with avoiding anunexpected data such as noise, and to effectively suppress a flickeringscreen due to light adjustment.

(3) Using the maximum value (the minimum value) of luminance of theimage signal as the feature, since these values can be shared with theexpansion coefficient (expansion parameter), the construction of theimage analyzing unit 34 may be simplified, thereby realizing a low cost.Further, there is an advantage in that, since an image area, where toneis collapsed due to the expansion process, can be suppressed to aminimum, it is possible to obtain a display faithful to the inputtedimage signal. Further, it is advantageous to simplify the constructionof the image-analyzing portion 34 since the maximum value and theminimum value of luminance of the image signal can be obtained withoutproducing a histogram.

The expansion coefficient and the offset value calculated by thehistogram-analyzing unit 37 are supplied as an image control signal tothe image analyzing unit 31, and the expansion coefficient is suppliedas the light control signal to the output correcting unit (outputbalance correcting means) 32.

The output correcting unit 32 has a lookup table (RGB-LUT) for givingpower-irradiation characteristic of the lamps 7R, 7G and 7B comprised inthe respective light sources 2R, 2G and 2B, and is adapted to input theoutput value of the light source determined based on the inputtedexpansion coefficient to the lookup table, and output it by referring tothe practical output value of each of the light sources 2R, 2G and 2B.Using this configuration, it is possible to carry out proper lightadjustment in which the variation in the light emitting flux due to theoutput property of the lamps 7R, 7G and 7B is corrected. Further, it ispossible to suppress variations in the white balance of the projectionimage due to light adjustment, and to obtain high quality displayedimage.

An example of the lookup table is shown in Table 1 below. Although thislookup table may store pre-measured output property of the light sources2R, 2G and 2B as an initial value, it may measure and store the outputproperty upon turning on or initiating the projection type displaydevice. With such a construction for updating the lookup table at anytime, it is possible to flexibly correspond to a slight propertyvariation of the light sources 2R, 2G and 2B, thereby obtaining stableimage quality over a long period.

TABLE 1 INPUT OUTPUT R OUTPUT G OUTPUT B  0  16  64  14  1  17  66  16 2  18  69  20 . . . . . . . . . . . . 253 253 1019 243 254 254 1021 248255 255 1023 250

In the case of the present embodiment, as shown in Table 1, the signalresolution of the light control signal corresponding to the light source2G of the green colored light component becomes higher as compared tothat of the light sources 2R and 2B corresponding to the red coloredlight component and the blue colored light component. Specifically, thelight control signal corresponding to the light source 2R and the lightcontrol signal corresponding to the light source 2B are 8 bits,respectively, while the light control signal corresponding to the lightsource 2G consists of 10 bits. Thus, the signal resolution of the lightcontrol signal becomes higher with respect to the light source 2G foroutputting the green colored light component with a human's highrelative luminous efficiency, and the output control is carried out morefinely, resulting in an improvement in substantial gray scale display tothe observer (audience). In other words, because it is possible to allowan observer to recognize the fine control on different colors bycarrying out fine control on a color with a high relative luminousefficiency in which an observer sensibly recognizes a variation inluminance or chroma (chromaticity), it is possible to simplify thecircuit construction of the output correcting unit 32 as compared to acase of adopting all signal resolution of the light control signalcorresponding to three colors to be 10 bits, and to realize a projectiontype display device with excellent tone display at a low cost.

Subsequently, the light control drivers 15 to 17 control the output ofeach of the light sources 2R, 2G and 2B based on each light controlsignal supplied from the output-correcting portion 32. In the projectiontype display device of the present embodiment, since the lamps 7R, 7Gand 7B of the light sources 2R, 2G and 2B are configured of lightemitting diodes, the light flux can be adjusted by the light emittingamount of each light emitting diode element in changing the light fluxbased on the light control signal. Therefore, it is possible to effectproper light adjustment easily, and also to carry out excellent temporalcontrollability by the high-speed response of the light emitting diodeelement.

On the other hand, the image-processing portion 31 comprises an offsetprocessing unit 41 and an expansion-processing portion 42, as shown inthe block diagram of FIG. 5.

The offset processing unit 41 is adapted to independently carry out anoffset process on color signals (i.e., the R signal, the G signal, the Bsignal) corresponding to colored light components of respective lightsources 2R, 2G and 2B separated from the inputted image signal, based onthe offset value supplied from the image analyzing unit 34. This offsetprocess is a process for subtracting the offset value extracted based onthe histogram as shown in FIG. 4 from the image signal, and unnecessarydilute black drift in the display can be prevented by carrying out sucha process. The offset value is set to, for example, the luminance (thegray scale value) of the darkest pixel of the image data of one frame ora predefined luminance (gray scale value), and black is darkened byintentionally collapsing the tone in an area having a luminance darkerthan the set luminance, thereby obtaining display with dark black.

The expansion processing unit 42 is adapted to independently carry outan expansion process on each of the color image signals (the R signal,the G signal and the B signal) subjected to the offset process, based onthe expansion coefficient supplied from the image analyzing unit 34.This expansion process is a process of expanding an amplitude of theinputted image signal (color signal) to a dynamic range width of theliquid crystal light valve, and by carrying out such a process, displaycontrast can be improved using the dynamic range of the liquid crystallight valve fully.

In addition, an R′ signal, a G′ signal and a B′ signal outputted fromthe expansion processing unit 42 are supplied to respectivecorresponding light valve drivers 12 to 14, and the liquid crystal lightvalves 22 to 24 are controlled by the light valve drivers 12 to 14, sothat the respective colored light components are modulated.

Thus, in the projection type display device of the present embodiment,in order to carry out the display by changing the light flux, outputs oflight sources 2R, 2G and 2B comprising the light emitting diodes as thelamps 7R, 7G and 7B are changed by the light control signal based on theinputted image signal, and then it is unnecessary to considerreliability or durability such as deterioration of the light adjustingelement due to light irradiation or deterioration of a mechanicalstructure of the shutter, as in the case of carrying out lightadjustment by blocking the light from a light source using a liquidcrystal light adjustment element, a mechanical shutter or the like, andit is possible to provide a projection type display device with highreliability in a simplified construction. Further, because there is nolight emitting spectral variation in the light emitting diode element bywhich output variation is accompanied as in the white light source, itis possible to carry out light adjustment while maintaining color tonewithout using a large sized correcting circuit, and then it isadvantageous to make the display device at a low cost.

In addition, in operation of the projection type display device, theimage processing parameter supplied by the image analyzing unit 34 maybe employed as a parameter for an image signal of a subsequent frame inthe image processing unit 31, and the image processing may be carriedout in real time by delaying image signal transmission to the imageprocessing unit 31 by the steps of the image analyzing unit 34 using aframe memory.

Although the configuration in which light components outputted from theliquid crystal light valves 22 to 24 are mixed by the dichroic prism 25,which is a color mixing system and are outputted to the projectionsystem 26 is shown and described in the embodiment, the configurationsas shown in FIGS. 6( a) and 6(b) may be adopted as the projection typedisplay device according to the present embodiment.

The projection type display device as shown in FIG. 6( a) includes threelight sources 2R, 2G and 2B in parallel arrangement, liquid crystallight valves 22 to 24 disposed correspondingly to respective lightsources 2R, 2G and 2B, and projection systems 45 to 47 arranged at oneside of the liquid crystal light valves 22 to 24. In this projectiontype display device, light component modulated by the liquid crystallight valves 22 to 24 is projected on the screen 27 by three projectionsystems 45 to 47, and the displayed image is imaged on this screen. Thelight sources 2R, 2G and 2B, and the liquid crystal light valves 22 to24 have the same construction as that of each element as shown in FIG.1.

Even in the projection type display device comprising theabove-described construction, an image processing unit (not shown inFIG. 6) for carrying out a predetermined image processing on eachcolored light component is connected to each of the liquid crystal lightvalves 22 to 24, and the image signal subjected to the predeterminedimage processing in the image processing unit is supplied to each of theliquid crystal light valves 22 to 24 via the light valve drivers.Further, an image analyzing unit (not shown) is coupled to the lightsources 2R, 2G and 2B via the light control drivers, and controls theoutput of each of the light sources 2R, 2G and 2B based on image signalanalysis by the image analyzing unit. In addition, by carrying out alight adjustment display to which the above-described light adjustingmethod according to the present invention is applied, it is possible torealize rich tone display by enlarging the substantial dynamic range, asin the projection type display device according to the aforementionedembodiment.

On the other hand, the projection type display device as shown in FIG.6( b) is a single panel projection type display device comprising anillumination system 120 having light sources 121R, 121G and 121Bcomposed of light emitting diodes made to emit different colored lightcomponents, a liquid crystal light valve 125, and a projection system126.

In addition, in the projection type display device comprising theconstruction, an image processing unit (not shown in FIG. 6) forcarrying out a predetermined image process on each colored lightcomponent is connected to the liquid crystal light valve 125, and theimage signal subjected to the predetermined image process in the imageprocessing unit is supplied to each liquid crystal light valve 125 viathe light valve driver. Further, an image analyzing unit (not shown) isconnected to the light sources 121R, 121G and 121B via the light controldrivers, and controls the output of each of the light sources 121R, 121Gand 121B based on image signal analysis by the image analyzing unit. Inaddition, by carrying out a light adjustment display to which theabove-described light adjusting method according to the presentinvention is applied, it is possible to realize smooth gray scaledisplay by enlarging the substantial dynamic range, as in the projectiontype display device of the aforementioned embodiment.

In the case of the projection type display device comprising theconstruction as shown in FIG. 6( b), it is possible to realize two typesof display manners of (1) a construction using the liquid crystal lightvalve 125 for a monochrome display, and (2) a construction using theliquid crystal light valve 125 for a color display.

(1) In the case of adopting the liquid crystal light valve 125 for themonochrome display, a color image is imaged on the projected screen bytime-sequentially emitting the light sources 121R, 121G and 121B (e.g.,for one 180th second) and displaying a content synchronized to the lightemitting timing of each colored light on the liquid crystal light valve125.

Since the projection type display device of the present embodimentincludes light emitting diodes as the light sources 121R, 121G and 121B,it is possible to very easily carry out the switching of the output ofthe light source time-sequentially and also to make excellent temporalcontrollability.

(2) In the case of adopting the liquid crystal light valve 125 for thecolor display, a display is carried out by continuously emitting thelight sources 121R, 121G and 121B and by irradiating a white coloredlight component produced by a mixed color to the liquid crystal lightvalve 125.

Since the projection type display device of the present embodiment caninclude light emitting diodes as the light sources 121R, 121G and 121B,it is possible to easily carry out the correction of white balance byindependently controlling the output of each light source even thoughthe white balance is changed due to light adjustment.

Next, the second embodiment of the invention will be described withreference to FIG. 7. The display device of the present embodiment is aprojection type display device comprising an optical system as in theprojection type display device of the first embodiment shown in FIG. 1,and a drive circuit shown in FIG. 7.

FIG. 7 is an exemplary block diagram of a projection type display deviceaccording to the present embodiment, and a difference from the blockdiagram shown in FIG. 2 is that an image analyzing unit 44 is disposedinstead of the image analyzing unit 34, and a plurality of light controlsignals from the image analyzing unit 44 is supplied to the lightcontrol drivers 15 to 17.

The image analyzing unit 44 according to the present embodiment caninclude a configuration representing its block diagram in FIG. 8, andcomprises histogram-producing units 36 a to 36 c for producing eachhistogram based on R signal, G signal and B signal divided from theimage data of an image signal inputted in a predetermined period, andhistogram-analyzing units 37 a to 37 c for analyzing each producedhistogram. In addition, an expansion coefficient (image control signaland light control signal) and an offset value (image control signal)calculated by the histogram-analyzing units 37 a to 37 c are supplied tothe image processing unit 31 and the light control drivers 15 to 17.

The present embodiment is adapted to be divided to color signalscorresponding to the colored light components outputted from the lightsources 2R, 2G and 2B before the image signal is inputted to thehistogram-producing units 36 a to 36 c, but the signal resolution of theG signal is composed of 10 bits, and the signal resolution of the Rsignal and the B signal is composed of 8 bits, respectively, upon thissignal division. In addition, a histogram is produced for each of thecolor signals inputted to the histogram-producing units 36 a to 36 c.

FIG. 9 illustrates an example of a histogram produced in the imageanalyzing unit 44 according to the present embodiment, and FIGS. 9( a)to (c) illustrate histograms produced from the R signal, the G signal,and the B signal, respectively. In the histogram shown in FIGS. 9( a) to9(c), a horizontal axis indicates a gray scale level and a longitudinalaxis indicates the number of pixels.

In addition, the histogram-analyzing units 37 a to 37 c analyze thethree supplied histograms, respectively, and calculate the expansionparameters (expansion coefficients) corresponding to the respectivelight sources 2R, 2G and 2B independently. That is, the expansionparameter indicated by a triangle marker in the horizontal axis of FIG.9 are set for each of the R signal, the G signal and the B signal. InFIG. 9, a case is shown where a gray scale level of the pixel subtracted(counted) by a predetermined pixel number (e.g., 10%) from a pixel of amaximum gray scale level is adopted as the expansion parameter.

Subsequently, the histogram-analyzing units 37 a to 37 c supply theexpansion coefficient as a light control signal to respective lightcontrol drivers 15 to 17. In addition, the output of each of the lightsources 2R, 2G and 2B is controlled by each of the light control drivers15 to 17.

The image analyzing method described in the first embodiment can beapplied to the histogram analysis in the histogram-analyzing units 37 ato 37 c. Further, in the case of the present embodiment, since thehistogram analysis is carried out for a histogram corresponding to eachcolor signal, it is possible to derive an image processing parameter bychanging the extraction methods from the histogram for each histogram.By allowing the feature for setting the image processing parameter to bechanged for each histogram as described above, it becomes possible toset the image processing parameter more flexibly and accurately, therebypromoting improved image quality of the displayed image upon lightadjustment.

On the other hand, the image processing unit 31 carries out apredetermined image process on the image signal by the offset processingunit 41 and the expansion processing unit 42 shown in FIG. 5, based onthe expansion coefficient and the offset value received from thehistogram-analyzing units 37 a to 37 c. In the case of the presentembodiment, because an image control signal for each colored lightcomponent (color signal) is outputted from the image analyzing units 37a to 37 c, each different offset value is inputted to a block forprocessing each color signal in the offset processing unit 41 shown inFIG. 5, and also, each different expansion coefficient is inputted tothe block for processing each color signal in the expansion processingunit 42 as well.

The modified image signal is supplied to the light valve drivers 12 to13, and a display corresponding to each colored light component is madein each of the liquid crystal light valves 22 to 24.

Thus, even in cases in which there is deflection in distribution of eachcolored light component as shown in FIG. 9, by setting the expansionparameter for each colored light component in the projection typedisplay device of the present embodiment mode, it is possible to carryout the display in a suitable dynamic range width for each colored lightcomponent. As a result, it is possible to carry out the light adjustmenteffectively and accurately, thereby further promoting improved imagequality of the display.

In the case of the present embodiment as described above, with respectto signal resolution (bit width) of each color signal supplied to thehistogram-producing units 36 a to 36 c, the signal resolution of the Gsignal becomes higher as compared to other color signals. Thus, bycarrying out gray scale control more minutely on a green colored lightsignal having a human's high relative luminous efficiency, it ispossible to make a rich tone display of a display visually recognized byan observer without increasing the signal resolution of other colorsignals. Thus, it is possible to make a small-sized circuit of theimage-analyzing portion 44 for the R signal and the B signal. As aresult, it becomes a configuration advantageous to cost reduction of theprojection type display device.

Further, in carrying out the display by changing the light flux even inthe projection type display device of the present embodiment, since theoutputs of the light sources 2R, 2G and 2B comprising the light emittingdiodes as the lamps 7R, 7G and 7B are changed, it is unnecessary toconsider reliability or duration such as deterioration of the lightadjustment element due to light irradiation and deterioration of amechanical structure of the shutter, and it is possible to provide ahigh reliable projection type display device in a simplifiedconfiguration, as in the case of carrying out the light adjustment byblocking the light component from the light source by a liquid crystallight adjustment element, mechanical shutter or the like.

Further, since the light emitting diode element does not have lightemitting spectral variation by which output variation is accompanied asin a white colored light source, it is possible to carry out lightadjustment with maintained color tone without using a large scalecorrecting circuit, and it is advantageous to making a low cost displaydevice.

Although the form of the display device according to the invention hasbeen described by way of the projection type display device in the firstand second embodiments, it should be understood that the invention canbe also applied to a direct display device. Further, although liquidcrystal light valves are used as a light modulating device in theembodiment, DMD (digital maicro-mirror device) or the like may be usedas light modulating means.

1. A display device for displaying an image in accordance with an imagesignal, comprising: a plurality of light emitting diodes, each of whichoutputs different colored light components; an image analyzing deviceadapted to analyze the image signal, output a plurality of light controlsignals for controlling an output of each of the light emitting diodes,and calculate an expansion coefficient for expanding an amplitude of theimage signal; a light control device adapted to receive the lightcontrol signals and control the output of each of the light emittingdiodes based on the light control signals; an expansion processing unitadapted to expand the amplitude of the image signal based on theexpansion coefficient calculated by the image analyzing device; and alight modulating device adapted to modulate each of the colored lightcomponents in accordance with the image signal, the amplitude of whichhas been expanded.
 2. The display device according to claim 1, the imageanalyzing device outputting each of the light control signals based onan average value of a luminance of each of the color signals inputted ina predetermined period.
 3. The display device according to claim 1, theimage analyzing device outputting each of the light control signalsbased on a maximum value of a luminance of each of the color signalsinputted in a predetermined period.
 4. The display device according toclaim 1, the image analyzing device outputting each of the light controlsignals based on a luminance distribution of each of the color signalsinputted in a predetermined period.
 5. The display device according toclaim 1, the image analyzing device setting each of the light controlsignals using different features for each of the color signals.
 6. Thedisplay device according to claims 1, the image analyzing device beingable to output an image control signal to modulate the image signal, andthe display device including an image processing device that modulatesthe image signal of the displayed image based on the image controlsignal.
 7. An image display method for displaying an image in accordancewith an image signal, comprising: providing a plurality of lightemitting diodes, each of which outputs different colored lightcomponents; analyzing the image signal; outputting a plurality of lightcontrol signals for controlling an output of each of the light emittingdiodes based on analysis; calculating an expansion coefficient forexpanding an amplitude of the image signal; controlling the output ofeach of the light emitting diodes based on the light control signal;expanding the amplitude of the image signal based on the expansioncoefficient; and modulating each of the colored light components inaccordance with the image signal, the amplitude of which has beenexpanded.
 8. The light adjusting method of a display device according toclaim 7, the light control signal being set based on different featuresfor each of the color signals upon setting the light control signals inthe image analyzing step.